Ask A Scientist Chemistry Archive

name         Pat B.
status       other
age          40s

Question -   My car gets crepe myrtle stains on it from the crepe myrtle tree blossoms.  
They are a reddish/brown stain and is impossible to remove! Help! What can I rub on this to 
remove it easier?
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Stain removal -- one of the tougher applications of chemistry. There are two guiding principles:

1. Know what the chemical nature of the stain is.
2. Do not damage the object being treated. There are several principles at play, not all of 
which you may be able to control.
3. Always pre-test a treatment on a small inconspicuous area to test the removal procedure.
4. Be safe --  work in a cool ventilated area away from any sources of flame or ignition.


Always wear nitrile rubber gloves, not the thin "latex" gloves, to protect your hands.
    A) Keep the car as cool as possible. That may already be a moot point.
    B) Know the nature of the stain. Is it just pigment/dye from the crepe myrtle, or is a 
	"resinous" material that the tree exudes? In either case start with a "cold water" wash 
	of the car -- not the car wash with "steam" cleaning.
    C) Try the least aggressive treatment first (to minimize potential damage to the car 
	finish. First try mineral spirits (available from a hardware store. If the stain is 
	"resinous" the mineral spirits will soften the "goop" and the color will come off. Use 
	gentle rubbing after soaking for a short time, say about 1 minute. Be careful mineral 
	spirits is a flammable solvent, so work in good ventilation and away from sources of 
	ignition. Mineral spirits will not attack the car finish. Repeat this method with 70% 
	rubbing alcohol, available at any pharmacy -- the other precautions also apply here.
    Soak an area with an 'enzyme' type stain remover used in washing clothes. What this 
	treatment does is decompose proteins that may be present and thus loosen the stain. It 
	does not "remove" the stain itself, but destroys the protein that makes the stain hard to 
	remove. Enzyme treatments are used to remove grass stains in clothing. It should not damage 
	the finish.
    All of the above are not stain removers per se. They are attacking the matrix holding the 
	stain on the car finish.
    Next try some 3% hydrogen peroxide (available at any pharmacy). This is an effective stain 
	remover, often overlooked. Does wonders on blueberry and blood stains, so it is a good but 
	gentle oxidant that will not damage the car finish.
    If that does not work you will have to bring in the "heavy artillery". Dab some household 
	chlorine bleach on a small area. Let it soak for about 1 minute and wash off. If this works 
	do a small area at a time and rinse off, then move to another area. Do NOT mix the bleach 
	with household ammonia. That combination forms chloramines which are very acrid and toxic.
    If none of these 'home remedies' is effective you will have to throw in the towel and seek 
	an auto dealer or body shop. They can buff/polish the car. This will physically remove the 
	stains by removing a thin layer of the car finish.
    Do not park under any more trees.
	
Vince Calder
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Pat,

Much depends on the age of the car. In this response, I shall assume your car is less than 
ten years old. New car finishes are pretty tough. However, do not "rub" anything on new car 
paint. Abrasion will damage the clear-coat surface and then you will really have trouble. 
Instead, allow the chemistry of the cleaning agent to do the work -- in other words, gently 
wipe it on, allow it to work for a few seconds, and then gently wipe it off. I suggest you 
buy a small size container of a variety of new car surface cleaners. Try to avoid anything 
that claims to have polishing agents in their list of ingredients. I feel confident, if you 
try enough different kinds, you will find something that will meet your needs. When you do, 
buy lots of the stuff. A final word: It will be easier to remove the stains while they are 
still wet and before the sun has a time to fry them into the finish. Good luck.

Regards,
ProfHoff 706
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